1. Field of the Invention
The present invention relates to a lighting device for a vehicle having a rod shaped light guide member which emits lights in a linear form.
2. Description of the Related Art
As a lighting device for a vehicle which illuminates an inner part and an outer part of the vehicle, for instance, a lighting device shown in FIG. 4 is known. This lighting device 50 for a vehicle includes a rod shaped light guide member 51, a light source 53 and a guide case 55. The rod shaped light guide member 51 is formed with a transparent resin in the shape of a rod and has an incident surface 52 of lights on an end face. The light source 53 is formed with a semiconductor element such as a light emitting diode (LED) mounted on, for instance, a substrate 54. The light source 53 is arranged under a state that the light source is opposed to the incident surface 52 of the rod shaped guide member 51. The guide case 55 is provided with a tubular holding part 56 having both ends opened. An end part 51a of the rod shaped light guide member 51 is inserted into the holding part 56 so that the end part 51a is positioned. Then, when the light source 53 is turned on, lights emitted from the light source 53 are incident on the rod shaped light guide member 51 through the incident surface 52. When the lights are propagated in the rod shaped light guide member 51, the rod shaped light guide member 51 emits lights in a linear form to illuminate surroundings.
In the lighting device 50 for a vehicle, as the rod shaped light guide member 51 is more distant from the light source 53, a quantity of the lights incident on the rod shaped light guide member 51 through the incident surface 52 of the lights emitted by the light source 53 is more reduced. Accordingly, a light emission efficiency of the rod shaped light guide member 51 is deteriorated. Thus, the light source 53 is preferably allowed to come close to the rod shaped light guide member 51 from a view point of prevention of the light emission efficiency from being deteriorated.
As the above-described rod shaped light guide member 51, are exemplified a rod shaped light guide member formed with a plurality of members and having a layer structure that the plurality of members are laminated on concentric circles and a rod shaped light guide member formed with a single member and having no layer structure.
Further, the latter rod shaped light guide member 51 is roughly divided into two types. As disclosed in Japanese Patent No. 4463246, the rod shaped light guide member 51 as one of the types is provided with a reflection structure formed with a reflection surface such as a groove in an outer part of a molded body of a transparent resin. In the rod shaped light guide member 51 of this type, lights incident from an incident surface are reflected and scattered by the reflection surface of the groove, and accordingly, the lights are outputted from another surface, so that the lights are emitted in a liner form.
As disclosed in Japanese Patent No. 5341391, the rod shaped light guide member 51 of the other type is formed with light scattering particulates which are dispersed. In the rod shaped light guide member 51 of this type, the lights which are allowed to be incident from an incident surface 52 are scattered by the light scattering particulates to emit lights in a linear form.
In recent years, the lighting device 50 for a vehicle having the above-described structure is applied not only to a relatively dark illumination, but also to a lighting device for a vehicle which requires a brightness to illuminate an outer part of the vehicle. Thus, a voltage applied to the light source 53 is increased, so that a quantity of heat generation of the light source 53 is liable to increase. Accordingly, there is a fear that when the light source 53 is allowed to come close to the rod shaped light guide member 51, if heat of the light source 53 is transmitted to the rod shaped light guide member 51 through the incident surface 52, the rod shaped light guide member 51 may possibly undergo a thermal damage depending on a space between them. For instance, in the case of the rod shaped light guide member 51 having no layer structure, the rod shaped light guide member 51 is softened. Further, in the case of the rod shaped light guide member 51 having the layer structure, there is a fear that an interlayer peeling may possibly arise due to heat. In this case, a difference arises in a light scattering property or transparence between a peeling part and other parts than the peeling part.